Independent power generation in aircraft

ABSTRACT

Systems and methods of independent power generation are disclosed. A particular system includes an aircraft having at least one engine and a plurality of independent power units. Each power unit of the plurality of independent power units generates electricity independently of the at least one engine. The plurality of independent power units include at least a first independent power unit that generates first electricity having a first set of electrical characteristics and a second independent power unit that generates second electricity having a second set of electrical characteristics concurrently with the first power unit generating the first electricity. The first set of electrical characteristics is different than the second set of electrical characteristics.

FIELD OF THE DISCLOSURE

The present disclosure is generally related to independent generation ofpower in aircraft.

BACKGROUND

In current aircraft that employ jet engines, power is extracted from theengines to power various components of the aircraft. For example, theengines may be used to turn generators, compressors or pumps, via amechanical linkage to extract power directly from the engines. Inanother example, bleed air may be diverted away from a core of theengine for uses other than providing thrust to the aircraft. Powerextraction in high by-pass ratio turbofan engines may increase thrustspecific fuel consumption of these engines. In addition, idle speeds ofthese engines may be increased in order to provide sufficient power forthe aircraft during ground, decent, approach and landing phases offlight thus increasing specific fuel consumption of the engine.

SUMMARY

Systems and methods of independent power generation in aircraft aredisclosed. In a particular embodiment, an aircraft includes at least oneengine and a plurality of independent power units. Each power unit ofthe plurality of independent power units generates electricityindependently of the at least one engine. The plurality of independentpower units includes at least a first independent power unit thatgenerates first electricity having a first set of electricalcharacteristics and a second independent power unit that generatessecond electricity having a second set of electrical characteristicsconcurrently with the first power unit generating the first electricity.The first set of electrical characteristics is different than the secondset of electrical characteristics.

In another particular embodiment, a method includes generating thrust atone or more engines of an aircraft. The method further includesgenerating first electricity at a first power unit that is independentof the one or more engines of the aircraft. The method also includes,concurrently with generating the first electricity, generating secondelectricity at a second power unit that is independent of the one ormore engines of the aircraft.

In another particular embodiment, an aircraft includes a body that has afirst independent power unit. The first independent power unit providespower to a first set of powered devices. The body also includes a secondindependent power unit that provides power to a second set of powereddevices concurrently with the first independent power unit providingpower to the first set of powered devices. The first set of powereddevices is different than the second set of powered devices. Theaircraft also includes at least one engine coupled to the body. Neitherthe first independent power unit nor the second independent power unitreceives operational power from the at least one engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional architecture of an aircraft;

FIG. 2 is a diagram of an aircraft architecture to independentlygenerate power in an aircraft according to a particular embodiment;

FIG. 3 is a diagram of an embodiment of an aircraft with independentpower generation; and

FIG. 4 is a flow chart of a particular embodiment of a method ofindependently generating power in an aircraft.

DETAILED DESCRIPTION

The features, functions, and advantages that are described can beachieved independently in various embodiments disclosed herein or may becombined in yet other embodiments further details of which can be shownwith reference to the following description and drawings.

FIG. 1 is a block diagram of a conventional architecture of an aircraft100. In a particular configuration, the aircraft 100 includes a fuselage102, a plurality of wings 104, one or more engines 106, and landing gear108. The engines 106 generate thrust to propel the aircraft.Additionally, the engines 106 may be used to enable operation of variousaircraft systems. For example, a portion of the power generated by theengines 106 may be used to turn generators 120 to generate electricalpower. To illustrate, the generators 120 may be coupled to the engines106 via various mechanical linkages, such as transmission systems, toutilize rotation in the engines 106 to turn the generators 120 togenerate the electrical power. The electrical power may be distributedthroughout the aircraft 100 via one or more power interconnects 122 topower one or more powered systems 124 (labeled “MISC.” in FIG. 1 sincethe powered systems 124 could include any system of the aircraft 100that uses electrical power). In particular configurations, substantiallyall of the electrical power utilized in the aircraft 100 is generatedusing the generators 120 during normal operation (i.e., non-emergency,non-startup operations).

A portion of the power generated by the engines 106 may be used topressurize a hydraulic system. For example, a portion of the electricalpower generated by the generators 120 may be used at motors 126 tooperate pumps 128 that pressurize the hydraulic system. In anotherexample, the hydraulic system may be pressurized by pumps 132 that arecoupled to the engines 106 via mechanical linkages. That is, the pumps132 are operated by rotation of the engine 106 to pressurize thehydraulic system. The hydraulic system may power one or more hydraulicactuators 130 that move various aircraft components, such as flightcontrol surfaces. Depending on the particular configuration, the pumps128 or the pumps 132 may be supplemental or back-up systems that areoperated only when other pumps are not operational. To illustrate, thepumps 128 may pressurize the hydraulic system during normal (e.g.,non-emergency) operation; however, if the aircraft 100 experiences anelectrical power failure, the pumps 132 may pressurize the hydraulicsystem using power from the engines 106.

A portion of the power generated by the engines 106 may also be used forde-icing. For example, bleed air from the engines 106 may be provided toa cowl thermal anti-icing (CTAI) system 160. The CTAI systems 160 mayprovide de-icing functions at an engine nacelle housing each of theengines 106.

Bleed air may also be taken from the engines 106 to operate a pneumaticsystem. The pneumatic system distributes pressurized air to the aircraft100 to operate or to provide backup operation of various systems. Forexample, the pneumatic system may be used to power one or more turbines136 that operate pumps 138. The pumps 138 may pressurize the hydraulicsystem to operate various hydraulic devices, such as one or more of theactuators 130, the landing gear 108, or other system. The pneumaticsystem may also provide air to a wing de-icing system 140. The pneumaticsystem may provide pressurized air to an environmental control system(ECS) 142. The ECS 142 may include a heat exchanger (FIX) 144. The ECS142 may utilize the pressurized air and ram air to provide environmentalcontrols, such as cooling air to the fuselage 102 of the aircraft 100.The pneumatic system may also provide pressurized air to a nitrogengeneration system (NGS) 146 that generates nitrogen or nitrogen-enrichedair for use in providing an inert environment for one or more fuel tanks116.

To receive an Extended-range Twin-Engine Operational PerformanceStandards (ETOPS) rating, the aircraft 100 may also include an auxiliarypower unit (APU) 112. The APU 112 may power the electric distributionsystem. For example, the APU 112 may burn fuel from the fuel tanks 116to operate a generator 148 that is coupled to the power interconnects122. The APU 112 may provide power to one or more of the powered devices124, motors 126, etc., when the engines 106 are not operating or tosupplement power provided by the engines 106. The APU 112 may alsooperate a compressor 150 to pressurize the pneumatic system when theengines 106 are not operating or to supplement pressurization providedby the engines 106. The APU 112 may be started by power provided from amain battery 114. In certain configurations, the APU 112 is used tostart the engines 106.

To receive an ETOPS rating, the aircraft 100 may also include a ram airturbine (RAT) 110. The RAT 110 may provide emergency power to theaircraft 100 in the event of a problem with one or more of the engines106. For example, the RAT 110 may be turned by ram air to operate agenerator 152 coupled to the power interconnects 122 to provideemergency power to one or more of the powered devices 124, the motors126, etc. Additionally, the RAT 110 may operate a pump 154 to pressurizethe hydraulic system to operate one or more of the actuators 130, thelanding gear 108, or other hydraulic devices.

FIG. 2 is a diagram of an aircraft architecture to independentlygenerate power in an aircraft 200 according to a particular embodiment.In a particular embodiment, the aircraft 200 includes a fuselage 202, aplurality of wings 204, one or more engines 206, and landing gear 208.In a particular embodiment, the architecture of the aircraft 200 isarranged such that the engines 206 are only used to generate thrust topropel the aircraft 200 and to power nacelle systems 260 located atengine nacelles housing the engines 206. The nacelle systems 260 mayinclude, for example, nacelle de-icing systems. Other systems of theaircraft 200 may be powered by a plurality of power modules 280. In aparticular embodiment, one or more of the power modules 280 is a linereplaceable unit (LRU).

In a particular embodiment, the power modules 280 are independent orstand-alone power units. That is, each of the power modules 280 maygenerate electricity independently of the engines 206. Additionally,each of the power modules 280 may generate electricity independently ofother power modules 280. For example, the plurality of power modules 280may operate concurrently or at different times depending on operationalneeds of systems powered by each of the plurality of power modules 280.To illustrate, two or more of the power modules 280 may operateconcurrently to provide power to various powered systems 224. In anotherillustration, two or more of the power modules 280 may operateconcurrently during a first time period. However, during a second timeperiod, one or more of the power modules 280 may cease generating power.For example, the first time period may be a period of high power demandand the second time period may be a period of reduced power demand.Thus, during the first time period, supplemental power modules may beactive to provide supplemental power; however, during the second timeperiod, the supplemental power may not be needed and the supplementalpower modules may be idled or turned off.

In various embodiments, the power modules 280 may be of the same type,or two or more of the power modules 280 may be of different types. Thepower modules 280 may include any type or combination of powergeneration devices. For example, one or more of the power modules 280may include a mechanical power generation device, such as a rotatingengine (e.g., a centrifugal or axial turbine), a reciprocating engine(e.g., an internal combustion engines such as a diesel engine, agasoline engine, or an engine that utilize another type of fuel). Inanother example, one or more of the power modules 280 may include achemical power generation device, such as a fuel cells or a battery. Instill another example, one or more of the power modules 280 may includeanother power generation device, such as a solar cell or a nuclearreactor. The power modules 280 may include any number and combination ofmechanical, chemical or other power generation devices. For example, thepower modules 280 may include four mechanical power generation devices.In another example, the power modules 280 may include two mechanicalpower generation devices, a fuel cell and a nuclear reactor. In stillanother example, a first of the power modules 280 may be a diesel or gasgenerator, a second of the power modules 280 may be a fuel cell, and athird of the power modules 280 may be a gas turbine. Other combinationsof types of the power modules 280 are also possible.

In a particular illustrative embodiment, the engines 206 receive fuelfrom a main fuel system (such as fuel tanks in the wings 204, thefuselage 202, external tanks (not shown), or any combination thereof),and the power modules 280 receive fuel from an independent fuel system(shown in FIG. 3). Thus, one or more of the power modules 280 may beindependent from a fuel system that provides fuel to the engines 206.Additionally, one or more of the power modules 280 may receive fuel froma fuel system that is independent of a fuel system that provides fuel toone or more of the other power modules 280. In a particular embodiment,the power modules 280 use a different type of fuel than the engines 206.For example, the engines 206 may utilize a jet fuel whereas one or moreof the power modules 280 may utilize a diesel fuel. In a particularembodiment, one or more of the power modules 280 may use a differenttype of fuel than one or more of the other power modules 280. Forexample, a first of the power modules 280 may include a diesel generatorthat uses diesel fuel and a second of the power modules 280 may includea gas turbine that uses a jet fuel.

Each of the power modules 280 generate power having a particular set ofelectrical characteristics, such as a frequencies or frequency range, avoltage or voltage range, current type (e.g., alternating current ordirect current), and so forth. In a particular embodiment, two or moreof the power modules 280 generate power having different electricalcharacteristics. For example, a first of the power modules 280 maygenerate direct current (DC) and a second of the power modules 280 maygenerate alternating current (AC). In another example, the first of thepower modules 280 may generate power having a first frequency range andthe second of the power modules 280 may generate power having a secondfrequency range that is different from the first frequency range. Sincethe power modules 280 may be independent of the engines 206, the firstfrequency range, the second frequency range or both may be independentof an operating speed (e.g., frequency of rotation or a number ofrevolutions per minute (RPMs)) of the engines 206. In yet anotherexample, the first of the power modules 280 may generate power having afirst voltage range and the second of the power modules 280 may generatepower having a second voltage range that is different from the firstvoltage range.

The power generated by the power modules 280 may be provided to variouspowered devices of the aircraft 200, as described further below. Weightof the aircraft 200 may be reduced by positioning a particular powermodule 280 near one or more powered devices that have power requirementsthat substantially match the electrical characteristics of powergenerated by the particular power module 280. For example, when theparticular power module 280 generates 28 V DC power, the power modulemay be located near powered devices that require 28 V DC power. Thus,distribution wiring to distribute the power to the powered devices maybe reduced due to placement of the particular power module 280.Additional weight savings may be attained since the power is generatedwith electrical characteristics that substantially match the powerrequirements of the powered devices. For example, in FIG. 1, thegenerators 120 may generate AC power that is converted to DC power usinga rectifier. However, since one of the particular power modules 280generates DC power directly, no rectifier or other power conversiondevices may be needed, resulting in weight savings for the aircraft 200.Similar savings may be attained by providing power to other powereddevices from power modules 280 that generate power with electricalcharacteristics that substantially match power requirements of the otherpowered devices. Stated another way, weight savings may be attained bynatively generating power (i.e., without conversion operations) havingelectrical characteristics that substantially match power requirementsof devices to be powered.

In a particular embodiment, one or more of the power modules 280 iscoupled to starter/generators (SG) 220. The starter/generators 220 mayprovide electrical power to a power distribution system of the aircraft200. The electrical power may be distributed within the aircraft 200 viaone or more power interconnects 222 to power one or more powered systems224. For example, a portion of the power generated by the power modules280 may be used to power one or more motors 226 that operate pumps 228to pressurize a hydraulic system of the aircraft 200. The hydraulicsystem may drive one or more hydraulic actuators 230, the landing gear208, or other hydraulic components. In another example, a portion of thepower generated by the power modules 280 may be used to power one ormore electrical actuators 282. The hydraulic actuators, the electricalactuators, or any combination thereof, may move various aircraftcomponents, such as flight control surfaces.

In yet another example, a portion of the power generated by the powermodules 280 may be used to power a de-icing system 240. In a particularembodiment, the de-icing system 240 provides de-icing to the wings 204,and de-icing of the engine nacelles is be provided by the nacellesystems 260, e.g., using bleed air from the engines 206.

In still another example, a portion of the power generated by the powermodules 280 may be used to power an environmental control system (ECS)242. The ECS 242 may utilize ram air and a heat exchanger (HX) 244 totemperature condition air to provide environmental controls, such ascooling air, to the fuselage 202 of the aircraft 200. A portion of thepower generated by power modules 280 may be used to power a nitrogengeneration system (NGS) 246 that generates nitrogen or nitrogen-enrichedair that is used to provide an inert environment for one or more fueltanks of the aircraft 200.

In a particular embodiment, certain systems of the aircraft 200 may havedifferent power requirements than other systems. For example, certain ofthe powered systems 224 may have different power requirements than themotors 226. Accordingly, the power distribution system may includetransformers, rectifiers or other devices that modify electricalcharacteristics of the power (generically referred to here astransformers (XFR) 266). The transformers 266 may modify a frequency ofthe power, a voltage of the power, convert the power from AC to DC,convert the power from DC to AC, modify other characteristics of thepower, or any combination thereof. For example, the transformers 266 maymodify electrical characteristics of the power generated by one or moreof the power modules 280 to enable charging of the battery 214. Thetransformers 266 may also modify power provided by the battery 214 toenable the battery 214 to power one or more of the powered devices 224.

In certain embodiments, the transformers 266 may modify the electricalcharacteristics of the power generated by a first of the power modules280 to be substantially similar to the electrical characteristics of thepower generated by a second of the power modules 280. In theseembodiments, the first power module may act as a backup to the secondpower module. Thus, if the second power module encounters an operationalproblem, power from the first power module can be routed to the systemsthat are normally (i.e., during non-emergency circumstances) poweredfrom the second power module. Since the power modules 280 can back eachother up during emergencies, in at least one of these embodiments, theaircraft 200 may not have an auxiliary power unit, such as the APU 112of FIG. 1. Additionally, in at least one of these embodiments, theaircraft 200 may not have a ram air turbine (RAT), such as the RAT 110of FIG. 1. In at least one embodiment, the aircraft 200 may be certifiedfor extended range operations under the Extended-range Twin-EngineOperational Performance Standards (ETOPS) without an APU, without a RATor without both due to the capability of the power modules 280 to backeach other up. For example, the aircraft 200 may achieve an ETOPS-120rating authorizing twin-engine operation 120 minutes from a diversionsite, an ETOPS-180 rating authorizing twin-engine operation 180 minutesfrom a diversion site, or another ETOPS rating authorizing twin-engineoperation at another distance from a diversion site.

FIG. 3 is a diagram of an embodiment of an aircraft 300 with independentpower generation. In a particular embodiment, the aircraft 300illustrated in FIG. 3 includes the aircraft architecture described withreference to FIG. 2. The aircraft 300 includes a body 301 and at leastone engine (such as the engines 303) coupled to the body 301. Althoughthe aircraft 300 is illustrated in FIG. 3 in a manner that resembles acommercial airliner, the aircraft 300 is not so limited. Rather, invarious embodiments, the aircraft 300 includes a rotary wing aircraft, ablended wing body aircraft, a lifting body aircraft, or anotherheavier-than-air or lighter-than-air aircraft. The body 301 may includea portion or component of the aircraft 300 that is distinct from wingsand control surfaces and that includes cargo or passenger cabins, ifpresent. The body 301 may be pressurized or non-pressurized, or portionsof the body 301 may be pressurized and other portions of the body 301may be non-pressurized.

In a particular embodiment, the body 301 includes a fuselage, such asthe fuselage 202 of FIG. 2. In an illustrative embodiment, the body 301also includes fairings coupled to the fuselage. The aircraft 300 mayalso include a plurality of wings 302 coupled to the body 301. Theengines 303 may be coupled to the body (e.g., the fuselage), to one ormore of the wings 302 or to both. Each of the engines 303 may be housedin an engine nacelle 304. Fuel is provided to the engines 303 from oneor more main fuel storage and supply systems 305. For example, the mainfuel storage and supply system 305 may include fuel tanks housed in thewings 302, in the body 301, or in both.

In a particular embodiment, the aircraft 300 also includes a pluralityof independent power units, such as a first independent power unit 314,a second independent power unit 324 and a third independent power unit336. The independent power units 314, 324, 336 may generate power usedby various components of the aircraft 300 independently of the engines303. For example, the independent power units 314, 324, 336 may notreceive operational power from the engines 303. Additionally, in aparticular embodiment, the independent power units 314, 324, 336 maygenerate power independently of one another. In a particular embodiment,any combination of the independent power units 314, 324, 336 may operateconcurrently to produce power. Further, one or more of the independentpower unit 314, 324, 336 may act as a back up to one or more of theother independent power units 314, 324, 336. In a particular embodiment,no power used within the body 301 is derived from the engines 303. Forexample, no bleed air may be provided to the body 301 from the engines303. Similarly, no mechanical linkages at the engines 303 may be used togenerate electricity or to store mechanical energy (e.g., to pressurizedhydraulic or pneumatic systems) used in the body 301. Rather, in aparticular embodiment, the independent power units 314, 324, 336 maygenerate all of the power used by the aircraft 300 outside the enginenacelles 304. Accordingly, the engines 303 may provide thrust to theaircraft 300 with improved efficiency.

In a particular embodiment, each of the independent power units 314,324, 336 is part of a line replaceable unit (LRU), such as a first LRU310, a second LRU 320, and a third LRU 330, respectively. The LRUs 310,320, 330 may be wholly integrated systems that are replaceable as aunit. For example, each of the LRUs 310, 320, 330 may have couplingconnectors (such as plugs, wire harnesses, etc.) to connect the LRU 310,320, 330 to power and/or control systems of the aircraft 300.Additionally, each of the LRUs 310, 320, 330 may have structuralconnectors to physically couple the LRU 310, 320, 330 to the aircraft300 at a particular location designated for the LRU 310, 320, 330.Accordingly, when an LRU 310, 320, 330 or a component of the LRU 310,320, 330 (such as one of the independent power units 314, 324, 336)fails, the entire LRU 310, 320, 330 can be disconnected and removed fromthe aircraft 300 as a unit and replaced with a different LRU. In aparticular embodiment, the LRUs 310, 320, 330 may be interchangeable.For example, the first LRU 310 may be coupled to the aircraft 300 at afirst location and the second LRU 320 may be coupled to the aircraft 300at a second location. The first location may be remote from the secondlocation. The first LRU 310 may be removed as a unit from the firstlocation and reinstalled in the aircraft 300 at the second location inplace of the second LRU 320.

In a particular embodiment, one or more of the LRUs 310, 320, 330 mayinclude a power conversion system 332. In the particular embodimentillustrated in FIG. 3, the third LRU 330 includes the third independentpower unit 336 and the power conversion system 332. The thirdindependent power unit 336 may generate electricity having a first setof electrical characteristics (e.g., frequency, voltage, current, etc.).The power conversion system 332 may convert at least a portion of theelectricity generated by the third independent power unit 336 to have asecond set of electrical characteristics that is different from thefirst set of electrical characteristics.

In a particular embodiment, one or more of the LRUs 310, 320, 330utilizes fuel from a source other than the main fuel storage and supplysystem 305. For example, the first power unit 314 of the first LRU 310may be a fuel cell that uses a first fuel type provided by a first fuelstorage and supply system 312; the second power unit 324 of the secondLRU 320 may be a diesel generator that uses a second fuel type providedby a second fuel storage and supply system 322; and the thirdindependent power unit 336 of the third LRU 330 may be a gas turbinethat uses a third fuel type provided by a third fuel storage and supplysystem 334. In a particular embodiment, one or more of the fuel storageand supply systems 312, 322, 334 of the LRUs 310, 320, 330 isindependent of the main fuel storage and supply system 305. In anotherparticular embodiment, the main fuel storage and supply system 305 maybe used as a back up fuel storage and supply system for one or more ofthe LRUs 310, 320, 330.

In a particular embodiment, each of the LRUs 310, 320, 330 is upgradableas a unit. For example, advances in technology may cause a particulartype of power generation technology to be superior in one or more waysto a type of power generation technology used by one or more of thepower units 314, 324, 336. For example, the particular type of powergeneration technology may become lighter, more efficient, able to usecheaper fuel, more reliable etc. In that case, one or more of the LRUs310, 320, 330 may be removed and replaced with a new LRU that has a newpower unit that uses the particular power generation technology.Additionally, the new LRU may include a new fuel storage and supplysystem that provides fuel appropriate for the new power unit. Further,the new LRU may include a power conversion system to convert powergenerated by the new LRU to have desired electrical characteristics,such as electrical characteristics that substantially match powerrequirements of devices to be powered by the new LRU.

In a particular embodiment, the LRUs 310, 320, 330 are distributed atdifferent locations within the aircraft 300. For example, the first LRU310 may be physically located near a first set of powered devices 316that receive power from the first LRU 310; the second LRU 320 may bephysically located near a second set of powered devices 326 that receivepower from the second LRU 320; and the third LRU 330 may be physicallylocated near a third set of powered devices 338 that receive power fromthe third LRU 330. In a particular embodiment, one or more of the LRUs310, 320, 330 output power that has electrical characteristics thatsubstantially match power requirements of the respective powered devices316, 326, 338. For example, the first powered device 316 may use 28 Vdirect current (DC) power and the first LRU 310 may output approximately28 V DC power. The second powered device 326 may use 270 V DC power andthe second LRU 310 may output approximately 270 V DC power. Similarly,the third powered devices 338 may use 400 Hz, 230 V three-phasealternating current (AC) power and the third LRU 330 may outputapproximately 400 Hz, 230 V three-phase AC power. By locating one ormore of the LRUs 310, 320, 330 near the powered devices 316, 326, 338that receive power from the LRU 310, 320, 330 and that have powerrequirements that substantially match electrical characteristics ofpower generated by the LRU 310, 320, 330, weight associated with powerdistribution components (e.g., wiring) and power conversion components(e.g., rectifiers, transformers, etc.) can be reduced.

In a particular embodiment, one or more of the LRUs 310, 320, 330 mayact as a backup to one or more of the other LRUs 310, 320, 330. Forexample, as depicted in FIG. 3, the first LRU 310 may back up the secondLRU 320. To illustrate, the first LRU 310 may provide power to the firstpowered devices 316 and, when needed, to the second powered devices 326.Since the first powered devices 316 and the second powered devices 326may have different power requirements, a power conversion system may beprovided. For example, a transformer 318 may modify electricalcharacteristics of power output by the first LRU 310 to substantiallymatch power requirements of the second powered devices 326. However, ina particular embodiment, the first powered devices 316 and the secondpowered devices 326 may have substantially similar power requirements,in which case, no transformer 318 may be used.

FIG. 4 is a flow chart of a particular embodiment of a method ofindependently generating power in an aircraft, the method generallydesignated 400. The method 400 may be performed in an aircraft having anaircraft architecture (e.g., the architecture described with referenceto FIG. 2), such as the aircraft 300 of FIG. 3. The method 400 mayinclude, at 402, starting the one or more engines of the aircraft usingpower from a first independent power unit and, at 404, generating thrustat one or more engines of the aircraft. The method 400 also includes, at406, generating first electricity at the first independent power unit.The first independent power unit may be independent of the one or moreengines of the aircraft. For example, the first independent power unitmay generate the first electricity without receiving power from the oneor more engines. The first electricity has a first set of electricalcharacteristics.

The method 400 may also include, at 408, generating second electricityat a second independent power unit concurrently with generating thefirst electricity. The second independent power unit may be independentof the one or more engines of the aircraft. For example, the secondindependent power unit may generate the second electricity withoutreceiving power from the one or more engines. The second electricity mayhave a second set of electrical characteristics that are different thanthe first set of electrical characteristics. The method 400 alsoincludes, at 410, shutting down the second independent power unit. In aparticular embodiment, the first and second independent power unitsgenerate power concurrently during a first time period 412. For example,the first time period 412 may be a period of high power demand. Thesecond power unit may be shut down during a second time period 414. Thesecond time period 414 may be a period of reduced demand (e.g., relativeto the first time period 412). Thus, the power units may be operated inan efficient manner.

The illustrations of the embodiments described herein are intended toprovide a general understanding of the structure of the variousembodiments. The illustrations are not intended to serve as a completedescription of all of the elements and features of apparatus and systemsthat utilize the structures or methods described herein. Many otherembodiments may be apparent to those of skill in the art upon reviewingthe disclosure. Other embodiments may be utilized and derived from thedisclosure, such that structural and logical substitutions and changesmay be made without departing from the scope of the disclosure.Additionally, the illustrations are merely representational and may notbe drawn to scale. Certain proportions within the illustrations may beexaggerated, while other proportions may be reduced. Accordingly, thedisclosure and the figures are to be regarded as illustrative ratherthan restrictive.

Although specific embodiments have been illustrated and describedherein, it should be appreciated that any subsequent arrangementdesigned to achieve the same or similar purpose may be substituted forthe specific embodiments shown. This disclosure is intended to cover anyand all subsequent adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

The Abstract of the Disclosure is provided with the understanding thatit will not be used to interpret or limit the scope or meaning of theclaims. In addition, in the foregoing Detailed Description, variousfeatures may be grouped together or described in a single embodiment forthe purpose of streamlining the disclosure. This disclosure is not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, claimed subject matter may be directedto less than all of the features of any of the disclosed embodiments.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe scope of the present disclosure. Thus, to the maximum extent allowedby law, the scope of the disclosure is to be determined by the broadestpermissible interpretation of the following claims and theirequivalents, and shall not be restricted or limited by the foregoingdetailed description.

What is claimed is:
 1. An aircraft, comprising: at least one engine; aplurality of independent power units; and a fuselage, wherein each powerunit of the plurality of independent power units generates electricityindependently of the at least one engine during flight, the plurality ofindependent power units including at least a first independent powerunit that generates first electricity having a first set of electricalcharacteristics and a second independent power unit that generatessecond electricity having a second set of electrical characteristicsconcurrently with the first power unit generating the first electricity,wherein the first set of electrical characteristics is different thanthe second set of electrical characteristics, wherein the secondindependent power unit provides power to an environmental control system(ECS) configured to provide conditioned air to the fuselage, andwherein, during flight, the ECS is electrically and pneumaticallyisolated from the at least one engine.
 2. The aircraft of claim 1,wherein the first electricity includes direct current and the secondelectricity includes alternating current.
 3. The aircraft of claim 1,wherein the first set of electrical characteristics includes a firstfrequency range and the second set of electrical characteristicsincludes a second frequency range, wherein the first frequency range andthe second frequency range are different.
 4. The aircraft of claim 3,wherein the first frequency range and the second frequency range areeach independent of an operating speed of the at least one engine. 5.The aircraft of claim 1, wherein the first set of electricalcharacteristics includes a first voltage range and the second set ofelectrical characteristics includes a second voltage range, wherein thefirst voltage range and the second voltage range are different.
 6. Theaircraft of claim 1, wherein the first independent power unit includes afirst generator.
 7. The aircraft of claim 6, wherein the secondindependent power unit includes a second generator.
 8. The aircraft ofclaim 1, wherein the second independent power unit includes a fuel cell.9. The aircraft of claim 1, wherein the second independent power unitincludes a gas turbine.
 10. The aircraft of claim 1, further comprising:a main fuel storage and supply system to provide fuel to the at leastone engine; a first fuel storage and supply unit to provide fuel to thefirst independent power unit; and a second fuel storage and supply unitto provide fuel to the second independent power unit, wherein the firstfuel storage and supply unit and the second fuel storage and supply unitare independent of the main fuel storage and supply system.
 11. Theaircraft of claim 10, further comprising a line replaceable unit (LRU)comprising the first fuel storage and supply unit and the firstindependent power unit.
 12. The aircraft of claim 1, further comprisinga third independent power unit that generates third electricity having athird set of electrical characteristics concurrently with the firstpower unit generating the first electricity and concurrently with thesecond power unit generating the second electricity, wherein the thirdset of electrical characteristics is different than the first set ofelectrical characteristics and is different than second set ofelectrical characteristics.
 13. The aircraft of claim 12, furthercomprising a power conversion system, the power conversion systemoperable to modify the third electricity to have the first set ofelectrical characteristics or the second set of electricalcharacteristics.
 14. The aircraft of claim 1, further comprising: atleast one first powered system having a first set of power requirements,wherein the first set of electrical characteristics substantiallymatches the first set of power requirements; and at least one secondpowered system having a second set of power requirements, wherein thesecond set of electrical characteristics substantially matches thesecond set of power requirements.
 15. The aircraft of claim 14, whereinthe first independent power unit and the at least one first poweredsystem are coupled to the fuselage at a first location, wherein thesecond independent power unit and the at least one second powered systemare coupled to the fuselage at a second location, wherein the secondlocation is remote from the first location, wherein a plurality of wingsis coupled to the fuselage, and wherein the at least one engine iscoupled to at least one of the fuselage and one or more of the pluralityof wings.
 16. The aircraft of claim 1, wherein, during flight, no powergenerated by the at least one engine is routed for use at the fuselageof the aircraft.
 17. An aircraft, comprising: a body, comprising: afirst independent power unit that provides power to a first set ofpowered devices; and a second independent power unit that provides powerto a second set of powered devices concurrently with the firstindependent power unit providing power to the first set of powereddevices, wherein the first set of powered devices is different than thesecond set of powered devices, and wherein the second set of powerdevices includes an environmental control system (ECS) configured toprovide conditioned air to a fuselage of the aircraft; and at least oneengine coupled to the body, wherein, during flight, neither the firstindependent power unit nor the second independent power unit receivesoperational power from the at least one engine, and wherein, duringflight, the ECS is electrically and pneumatically isolated from the atleast one engine.
 18. The aircraft of claim 17, wherein the at least oneengine is housed in at least one engine nacelle, wherein power derivedfrom the at least one engine is not routed to operate systems of theaircraft located outside the engine nacelle, and wherein the powerderived from the at least one engine includes electric power, mechanicalpower, pneumatic power, or a combination thereof.
 19. The aircraft ofclaim 17, wherein the first independent power unit is located nearer tothe first set of powered devices than to the second set of powereddevices and wherein the second independent power unit is located nearerto the second set of powered devices than to the first set of powereddevices.
 20. The aircraft of claim 17, wherein the first independentpower unit provides backup power to the second set of powered devices.